Frantz U.S. Pat. No. 3,603,154 (Frantz '154) discloses a pressure gauge assembly for gauging one or more air pressure lines of a diesel locomotive, a gauge of which is both removable for repair or replacement and testable in situ by a gauge tester, such as disclosed in Frantz U.S. Pat. No. 3,557,602 (Frantz '602), without uncoupling the assembly from any connected pressure line. As explained in Frantz '154, pressure gauges previously had been testable in place but removable for repair or replacement only after they had been uncoupled from any pressure line to which they were connected. The gauge of Frantz '602 is removable without uncoupling pressure lines because releasably mountable on a mounting bracket permanently connectable to one or more pressure lines and containing in each connection a check valve automatically closable before either testing or removal of the gauge. The concern of the present invention is with a pressure gauge assembly having the capabilities of Frantz '154 and particularly adapted for use on rapid transit cars.